The present invention relates to a semiconductor device and method of manufacturing the semiconductor device, and more specifically, to a semiconductor memory having a floating gate.
An Electrically Erasable and Programmable Read Only Memory (EEPROM) having a floating gate and a control gate, a Metal Nitride Oxide Silicon (MNOS) memory which does not include the floating gate are conventionally known as a non-volatile semiconductor memory that holds stored information after power thereof is turned off. A flash memory is also well known as one of EEPROMs.
The control gate covers the floating gate and further extends beyond a peripheral area of a memory cell part.
A technique for reducing a resistance value of the control gate is known in which a metal silicide film is formed over the control gate. However, due to a steep slope on a side surface of the floating gate provided at an outermost end of the memory cell, a steep slope may be formed over a top surface of the control gate. If an insulation film remains at the steep slope part of the control gate, this results in a problem in that a part where the metal silicide film is not formed at the steep slope part. This leads to uneven resistance values of the control gates and thus results in deterioration in the semiconductor memory characteristics. Note that the insulation film remaining at the steep slope part of the control gate is, for example, the insulation film which is deposited such that the control gate is covered with the insulation film when a sidewall insulation film is formed over the sidewall of the control gate and which is removed by an etching back process. For the problem described above, a technique is known in which a sidewall insulation film is formed over both side surfaces of the floating gate, so that the steep slope of the top surface over the control gate can be alleviated. Moreover, another technique is also known in which a film thickness of each of the floating gates is adjusted, so that the steep slope of the control gate can be alleviated.